a. Field of the Invention
The present invention relates generally to electronic test circuitry and, more particularly, to circuitry for testing the ability of an intermediate range nuclear instrument to detect and measure a constant current and a periodic current.
b. Description of the Prior Art
Occasionally, malfunctions occur in the nuclear instruments used to measure ion chamber current. These nuclear instruments, in this case termed "intermediate range nuclear instrumentation", are essentially comprised of an input circuit, a current level measuring circuit and meter, a rate of change of level measuring circuit and meter, and internal test circuits. This current, at levels of between 10.sup.-11 amperes and 10.sup.-2 amperes is generated by the ion chamber and is proportional to the neutron flux (power level) in the nuclear reactor. Since multiple channels of instrumentation are used, the malfunctioning instrument can be removed and replaced with a spare known to be operational. The malfunctioning instrument is then repaired. Upon completion of repairs, test circuits internal to the instrument are used to check the instrument and confirm if the repair actions were successful.
In many instances, external current sources are not readily available to confirm proper instrument operation starting at the instrument's signal input connector. Because the internal test circuits do not check the instrument from its signal input under system conditions, an input fault may go undetected until the instrument is re-installed in the system.
Typical of the prior art is U.S. Pat. No. 4,782,242 to Kovacs which discloses a switching circuit for generating high voltage pulses utilizing an inductive coil. Some named uses for that switching circuit include the ignition of internal combustion engines, ignition of flash tubes, and in traffic control systems.
A solid state monitoring system is disclosed in U.S. Pat. No. 3,927,399 to Fuzzell which provides an operator of a machine with a sensible indication when the condition being monitored changes from one side of a predetermined level of operation to the other side of that level. In this known instance, the system utilizes a solid state integrated circuit timer for each critical level of condition to be detected, the timer being connected for astable oscillation and triggered into oscillation when the charge of a timing capacitor rises to the threshold level of the timer.
Oscillation of the timer then energizes an indicator, for example, a light-emitting diode, to provide a sensible indication to the operator.
However, in no known instance is there available a simple and readily usable test circuit for testing the ability of an instrument to detect and measure both a constant current and a periodic current pulse.